1. Technical Field
The present invention relates to an ultra-high-temperature heat treatment apparatus.
2. Related Art
An ultra-high-temperature heat treatment apparatus having an electric furnace for use in heat treatment of wafers or the like is known. An electric heater of a conventional heat treatment apparatus is comprised of a single one-piece heater element which is installed in a spiral or folded form on the inner wall surface of a heat insulator of the electric furnace, with its heat generating portion directly fixed to the heat insulator. With such a one-piece heater structure, the whole heater element must be replaced even if the heater element is partly damaged, which is costly.
The conventional heat treatment apparatus further includes a water-cooled metal manifold and a furnace tube made of SiC/CVD-SiC and disposed above the metal manifold, the furnace tube being adapted to receive wafers or the like. An O-ring is inserted into a fitting portion between the furnace tube and the metal manifold, so as to prevent intrusion of contaminants from the outside. With this arrangement, however, it is difficult to increase the length of a uniform temperature zone of the furnace tube, and the furnace tube can be subject to a great heat shock.
Although the conventional heat treatment apparatus is configured to prevent the conduction of high temperature heat from the furnace tube, a SiC buffer is solely provided therefor, so that a large amount of heat may be transferred downwardly of the furnace tube, resulting in increased cooling costs to prevent the heat conduction.
Furthermore, the conventional heat treatment apparatus is provided with a flange which is vertically moveable relative to the above-mentioned manifold. To seal between the manifold and the flange, an O-ring is fitted into a tapered groove (generally, a dovetail groove) formed in a flat portion of the flange. However, the O-ring subject to high temperature heat sometimes sticks on the manifold to be detached from the tapered groove of the flange.
The conventional heat treatment apparatus further comprises a separator for loading a wafer into an annular holder and for separating the wafer from the holder. The separator is configured to push the wafer upward to separate the wafer and push the wafer downward to load the same into the holder. However, the work efficiency of the separator is not satisfactory.
An object of the present invention is to provide an ultra-high-temperature heat treatment apparatus including an electric furnace having a heater comprised of heater elements adapted to be replaceable on one-heater-element basis, thereby reducing costs for repair of the heater. Preferably, the heat treatment apparatus can suppress undesired reactions between a heat-generating portion of each heater element and a heat insulator constituting a refractory lining of the electric furnace and suppress a contraction of the heat insulator, thereby providing the electric furnace with a prolonged service life.
Another object of the present invention is to provide an ultra-high-temperature heat treatment apparatus permitting a joining portion between a furnace tube and a manifold to be disposed in a high-temperature environment and providing an increased length of a uniform temperature zone. Preferably, the heat treatment apparatus is arranged to perform evacuation through a slit formed in an upper face of the manifold so as to tightly seal the joining portion and to reduce metal contamination.
A further object of the present invention is to provide an ultra-high-temperature heat treatment apparatus which can reduce heat conduction from a furnace tube by means of a heat insulating apparatus and make it easy to cool a buffer-installed portion of the heat-insulating apparatus at low costs.
A still another object of the present invention is to provide an ultra-high-temperature heat treatment apparatus capable of unremovably holding an O-ring disposed between a manifold and a flange which constitute a contamination control apparatus, thereby positively preventing contamination.
A still another object of the present invention is to provide an ultra-high-temperature heat treatment apparatus capable of easily separating a heat-treatment object, preferably a wafer, from an annular holder for holding the heat-treatment object, thereby improving work efficiency.
According to one aspect of the present invention, there is provided an ultra-high-temperature heat treatment apparatus which comprises an electric furnace including a heater comprised of heater elements which are replaceable independently of each other, each heater element being disposed so as not to be in close contact with an inner wall face of a heat insulator of the electric furnace.
With the heat treatment apparatus of this invention, the heater elements of the heater of the electric furnace can be replaced on one-heater-element basis, thereby extremely reducing costs for fabrication and repair of the heater.
Preferably, each heater element includes a heat-generating portion disposed along the inner wall face of the heat insulator so as not to be in close contact therewith, and a fixture portion fixed to the heat insulator.
With this preferred arrangement, it is possible to suppress undesired reactions between the heat-generating portion of each heater element and the heat insulator as well as a contraction of the heat insulator, thereby permitting the heater elements to perform a stable heat-generating action at high temperatures. In addition, the heat-generating portions of the heater elements are not subject to mechanical constraint and hence deterioration of their durability due to thermal deformation stress is less likely to occur, so that the heater has a prolonged service life.
According to another aspect of the present invention, there is provided an ultra-high-temperature heat treatment apparatus which comprises a furnace tube, which is preferably made of porous SiC/CVD-SiC, and a manifold made of quartz and disposed beneath the furnace tube.
With the ultra-high-temperature heat treatment apparatus of the present invention, the length of a uniform temperature zone of the furnace tube can be increased by the provision of the quartz manifold disposed beneath the furnace tube preferably made of porous SiC/CVD-SiC, and a heat shock applied to the SiC/CVD-SiC furnace tube can be relieved.
Preferably, a slit is formed in an upper face of the quartz manifold at which the quartz manifold is joined to the furnace tube, and the slit is communicated with a vacuum evacuation system.
With this preferred arrangement, intermediate evacuation can be made through the slit formed in a joining face between the furnace tube and the quartz manifold and communicating with a vacuum evacuator system, thereby sealing the joining face. In the case of the Sic/CVD-SiC furnace tube for use with the quartz manifold communicating with the evacuation system, especially, metal contamination can be suppressed.
According to a further aspect of the present invention, there is provided an ultra-high-temperature heat treatment apparatus which comprises a furnace tube preferably made of porous SiC/CVD-SiC and a heat-insulating apparatus fitted into the furnace tube for interrupting heat conduction from the furnace tube. The heat-insulating apparatus includes a SiC buffer and a quartz buffer disposed beneath the SiC buffer.
With the ultra-high-temperature heat treatment apparatus of this invention, downward heat conduction from the furnace tube preferably made of porous SiC/CVD-SiC can be suppressed by the heat-insulating apparatus, and the cooling of a buffer-installed portion of the heat-insulating apparatus can be made with ease at low costs.
According to a further aspect of the present invention, there is provided an ultra-high-temperature heat treatment apparatus which comprises a furnace tube preferably made of porous SiC/CVD-SiC and a contamination control apparatus disposed beneath the furnace tube for preventing contamination in the furnace tube. The contamination control apparatus includes a quartz manifold and a quartz flange disposed beneath the quartz manifold. The quartz manifold and the quartz flange are each formed into an annular shape having a slanted peripheral face and are joined at their slanted peripheral faces to each other. An O-ring is fitted into a recess formed in one of the slanted peripheral faces of the quartz manifold and the quartz flange.
With the ultra-high-temperature heat treatment apparatus of this invention, the O-ring is unremovably held between the quartz manifold and the quartz flange which constitute the contamination control apparatus, whereby contamination in the furnace tube can be positively prevented by the contamination control apparatus.
According to a still another aspect of the present invention, there is provided an ultra-high-pressure heat treatment apparatus which comprises a separator mechanism for separating a heat-treatment object from an annular holder, which is larger in outer diameter than the heat-treatment object, for holding the heat-treatment object. The heat-treatment object, which is preferably a wafer, is subject to heat treatment in a furnace tube preferably made of porous SiC/CVD-SiC. The separator mechanism includes a holding portion for holding an outer peripheral portion of the annular holder, and a base portion disposed in alignment with a center axis of the separator mechanism and having a height thereof greater than that of the holding portion and an outer diameter thereof smaller than an inner diameter of the annular holder.
With the ultra-high-temperature heat treatment apparatus of this invention, when the annular holder and the heat-treatment object, preferably a wafer, held by the annular holder are placed together on the separator mechanism, only the annular holder reaches a vertical level below the upper face of the base portion of the separator mechanism, while permitting the base portion to be inserted into a central hole of the annular holder, and, at that vertical level, the outer peripheral portion of the annular holder is held by the holding portion of the separator mechanism, whereas the heat-treatment object is supported on the upper face of the base portion of the separator mechanism. As a result, the heat-treatment object is separated from the annular holder. In this manner, the heat-treatment object and the holder can be separated from each other with ease by simply placing the heat-treatment object and the holder together on the separator mechanism.
Preferably, the separator mechanism includes a housing which supports the holding portion of the separator mechanism. The holding portion is formed into an annular shape having an inner diameter smaller than an outer diameter of the annular holder. The base portion of the separator mechanism has an annular base extension extending from a lower part of the base portion and having an outer peripheral part thereof supported by an upper face of the annular holding portion of the separation mechanism.
With this preferred arrangement, when the base portion of the separation mechanism is placed on the annular holding portion supported by the housing of the separation mechanism, the annular base extension is held at its outer peripheral part by the annular holding portion, so that the base portion is disposed in alignment with the center axis of the separation mechanism.
More preferably, the separation mechanism includes separation mechanism sections which are disposed at interval in a vertical direction of the housing. Each separation mechanism section includes an annular holding portion supported by the housing and a base portion having an annular base extension.
With this preferred arrangement, when an annular holder and a heat-treatment object held by the holder are placed together on a lowermost separation mechanism section after a base portion of the lowermost separation mechanism section is positioned by placing a corresponding annular base extension on a corresponding annular holding portion, the heat-treatment object and the holder are held by the base portion and the holding portion of the lowermost separation mechanism section, respectively, to be separated from each other. Then, an annular base extension of the next lowermost separation mechanism section is placed on a corresponding annular holding portion, and thereafter, a heat-treatment object and a holder are separately held by the separation mechanism section. By repeating the above procedure, a number of heat-treatment objects, preferably wafers, can be disposed at intervals vertically of the separation mechanism.
Furthermore, structural features of the aforementioned first to fifth aspects and their preferred variants can be combined in various manners.